Solid propellant composition with burning rate catalyst

ABSTRACT

FREE RADICALS THAT CATALYZE THE BURNING RATE OF PROPELLANTS. SPECIFICALLY, THE FREE RADICAL COMPOUND, 2,2-DIP PHENYLPICRYLHYDRAZYL, INCREASES THE BURNING RATE OF PROPEL LANT COMPOSITIONS COMPRISED OF THE SPECIFIED FREE RADICAL COMPOUND AND OTHER MAJOR PROPELLANT INGREDIENTS CONSISTING OF THE INORGANIC OXIDIZER AMMONIUM PERCHLORATE, POLYBUTADIENE BINDER, OPTIONAL CATALYSTS (E.G., N-BUTYL FERROCENE OR FE2O3) AND ALUMINUM METAL POWDER. PROCESSING AIDS (E.G., LECITHIN) AND CURATIVES MAY BE USED IN MINOR AMOUNTS IN THE BASIC FORMULATION OR AS AN ADDITIVE TO THE PROPELLANT COMPOSITION.

United States Patent 3,666,575 SOLID PROPELLANT COMPOSITION WITH BURNINGRATE CATALYST Harold M. Fisher, Charlotte, N .C., assignor to the UnitedStates of America as represented by the Secretary of the Army NoDrawing. Filed Mar. 10, 1970, Ser. No. 18,321

Int. Cl. C06d /06 US. Cl. 149-19 8 Claims ABSTRACT OF THE DISCLOSUREBACKGROUND OF THE INVENTION Much effort has been expended in the area ofcatalysis and means for promoting burning rates of propellants.Increased burning rates permit the expulsion of a larger amount ofenergy over a shorter period of time to thereby result in a higherimpulse or force to perform a desired function by propulsion means. Inmany instances the use of a relatively small amount of a catalystmaterial (e.g., 1-2% by weight) enables one to change a slower burningpropellant into a faster burning propellant. Catalyst materials of theprior art include iron oxide, copper, copper chromite, the organoironcompound, ferrooene, and other organometallic compounds. More recentlycarborane and carborane derivatives have been employed as catalystmaterials for propellants.

The present invention deals with a new class of compound and its use asa catalyst material. The new class of compound is classified as a freeradical and is nonmetallic.

An object of this invention is to employ a free radical material whichis a non-metallic material yet a burning rate promoter for solidpropellants.

Another object is to provide solid propellant formulations which utilizea free radical material to enhance the propellant burning rate when thefree radical is used alone or with other catalyst materials incombination with the major propellant ingredients consisting of theinorganic oxidizer ammonium perchlorate, a polybutadiene binder, andaluminum metal powder.

SUMMARY OF THE INVENTION When 2,2-diphenylpicrylhydrazyl is used in apropellant formulation containing ammonium perchlorate, polybutadienebinder, lecithin (processing aid), and aluminum metal powder, thepropellant burns at a higher rate as compared to a standard propellantformulation containing all the specified constituents except the freeradical, 2.2- diphenylpicrylhydrazyl. The burning rates of a propellantcontaining other burning rate catalysts (e.g., n-butyl ferrocene or P 0are also increased when 2,2-diphenylpicrylhydrazyl is used as anadditional ingredient.

The amount of the free radical compound, 2,2-diphenylpicrylhydrazyl, maybe varied from about 0.5 percent by weight to about 5 percent by weightof the propellant composition.

The burning rate of the propellant increases with in creased2,2-diphenylpicrylhydrazyl content. The amount of ice the free radicalcompound may be optimized to achieve a desired burning rate either alonewith other propellant ingredients or in combination with other specifiedburning rate catalysts and other propellant ingredients.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The free radical,2,2-diphenylpicrylhydrazyl, is used alone or in combination with othercatalysts to increase the burning rate of propellants. The free radical,2,2-diphenylpicrylhydrazyl, is illustrated by the following structuralformula:

N 03 e\ r l t s I !Propellant formulations are set forth below underExamples I, H, -]II, IV, and V to illustrate the use of 2,2diphenylpicrylhydrazyl as a burning rate catalyst. Under Example I,below, control propellant A contains no catalyst; novel propellant Acontains 2,2-diphenylpicrylhydrazyl as catalyst.

EXAMPLE I Control Nove propellant propellant A A Ingredients, percent byweight:

Carboxy terminated polybutadiene 24. 7 21.7 Lecithin .1. 0.3 0.3Aluminum metal powder l l1. 6 11. 6 Ammonium perchlorate (17,1). 19.019.0 Ammonium perchlorate (200p) 44. 4 44. 4 2,2diphenylpicrylhydrazyl3. 0

Totals 100. 0 100. 0

(Burning rate ln./sec. at 500 p.s.i.g.) 191 .230 (Burning rate in./sec.at 1000 p.s.i.g.) 283 .312

As evidenced by the above burning rates an average of about 15 percentimprovement in burning rate is accomplished when 3 percent by weight ofthe binder of the uncatalyzed propellant is replaced with 3 percent byweight of 2,2-diphenylpicrylhydrazyl.

Example II below, sets forth control propellant B and novel propellant Bto illustrate the use of 2,2-diphenylpicrylhydrazyl in combination witha standard catalyst material, n-butyl ferrocene, to achieve improvedburning rates.

EXAMPLE Ii The above burning rates indicate that additional improvementin burning rates is achieved when 3 percent by weight of the binder ofthe n-butyl ferrocene catalyzed type propellant is replaced with 3percent by weight of 2,2-diphenylpicrylhydrazyl. The percent increase inburning rate varied from about 10.5% to 5.1% to 4.3% at the pressures of500, 1000 and 1500 p.s.i.g. respectively.

Example III, below, sets forth control propellant C and novel propellantC to illustrate the use of 2,2-diphenylpicrylhydrazyl in combinationwith a standard catalyst material, Fe O to achieve improved burningrates.

EXAMPLE III Control Novel propellant C propellant Ingredients, percentby weight:

Carboxy terminated polybutadiene 21. 7 18.7 Lecithin 0. 3 0.3 F6203 3. 03.0 Allumlnuln metal powder 11.6 11.6 Ammonium perchlorate (17p) 19. 0l9. 0 Ammonium perchlorate (200p) 44.4 44. 4 2,2-diphenylpicrylhydrazyl.3. 0

Totals 100.0 100. 0

(Burning rate in./sec. at 500 p.s.i.g.) 317 351 (Burning rate ln./sec.at 1000 p.s.i.g.) 407 505 (Burning rate in./sec. at 1500 p.s.i.g.) .483573 It is noted that the improvement in burning rates, when2,Z-diphenylpicrylhydrazyl is used in addition to Fe O is about 11%,24%, and 19% at the pressures 500, 1000, and 1500 p.s.i.g. respectively.

Example IV, below, sets forth control propellant D and novel propellantD to illustrate the use of 2,2-diphenylpicrylhydrazyl in combinationwith a standard catalysts, Fe O Smaller particle sized ammoniumperchlorate is used in the control propellant D and the novel propellantD. It is noted that the control propellant D burns at a higher rate. Itis also noted that additional improvement in burning rate is achievedwhen 2,2-diphenylpicrylhy- The percent improvement in burning rate ofthe novel propellant D, containing 3 percent by weight2,2-diphenylpicrylhydrazyl, is 14%, 15%, and 11% at the respectivepressures of 500, 1000, and 1500 p.s.i.g.

Example V, below, sets forth control propellant E and novel propellant Eto illustrate the use of 2,2-diphenylpicrylhydrazyl in combination witha standard catalyst, Fe O Smaller particle sized ammonium perchlorate isused in the control propellant E and the novel propellant E. Althoughnovel propellant E contains only 1%, 2,2- diphenylpicrylhydrazyl, animprovement burning rate is achieved.

EXAMPLE V Control propellant E Novel propellant E Ingredients, percentby weight:

Carboxy terminated po1ybutadiene. 20. 7 19. 7 Lecithin 0. 3 0. 3

(Burning rate inJsec. at 500 p.s.i.g.) 0. 715 0. 776 (Burning ratein./sec. at 1000 p.s.i.g. 1. 030 1. 090 (Burning rate in./sec. at 15 0p.s.i.g.) 1. 350 1. 400

The percent improvement in burning rate for novel propellant E is about84%, 5.8%, and 3.7% at the pressures of 500, 1000, and 1500 p.s.i.g.respectively.

No special procedures are required for the mixing of the propellantsamples other than standard methods or procedures employed in the art.For example, the polybutadiene, lecithin, catalyst material, andaluminum are blended in a mixer in the order listed after which theinorganic oxidizer is added in increments and throughly mixed untiluniform. The curing agents, cross linking agents or other additives aregenerally added and thoroughly blended with the mix just prior tocasting into a suitable mold or rocket motor. Generally, mixing duringthe last part of the mixing operation and casting operation isaccomplished under vacuum to eliminate air entrapment or voids in thepropellant. The temperature of the mix is generally maintained in therange of about F. F. A temperature in the range specified serves tomaintain a satisfactory viscosity during mixing and casting procedures.

The propellant formulations of this invention using carboxy terminatedpolybutadiene are cured by the curatives such as diaziridines,triaziridines, diepoxides, triepoxides, and combinations of the same. Anamount of curing agent up to about 2 percent by weight of all thecombined propellant ingredients is sufiicient for curing. The amount ofcuring agent used is dependent uopn the curing time, the curingtemperature, and the final physical properties desired for thepropellant.

The free radical compound, 2,2-diphenylpicrylhydrazyl, is not to belimited to its use with carboxy terminated polybutadiene binders. Otherbinder materials such as hydroxy or epoxy terminated polybutadienes, andthe copolymer such as polybutadiene-acrylic acid or the copolymerpolybutadiene acrylic acid-acrylonitrile are compatible with the freeradical compound, 2,2-diphenylpicrylhydrazyl. Therefore, the improvementin burning rate of a propellant employing ammonium perchlorate oxidizeralong with the binder types specified is likewise proportional to the2,Z-diphenylpicrylhydrazyl content as illustrated herein. By properselection of conventional curing agents for the binder material selected(e.g., polyisocyanates for the hydroxy or epoxy terminated) curing ofthe propellant is readily accomplished.

The propellant compositions of this invention contain the free radicalcompound, 2,2-diphenylpicrylhydrazyl, as catalyst, from about 0.5 toabout 5 percent by weight of the composition, inorganic oxidizer ofammonium perchlorate from about 50 to about 72 percent by weight of thepropellant composition, polybutadiene binder from about 10 to about 24weight percent by weight of the propellant composition, aluminum metalpowder from about 5 to about 15 percent by weight of the propellantcomposition, and lecithin from about 0.2 to about 0.5 percent by weightof the propellant composition.

Also, the propellant composition may contain an optional catalystmaterial selected from n-butyl ferrocene and Fe O for use with2,2-diphenylpicrylhydrazyl. The optional catalyst material may be usedin amounts up to about 5 percent by weight of the propellantcomposition. Curatives may be employed as an additional ingredient up toabout 2 percent by weight of the combined propellant ingredients.

I claim:

1. A solid propellant composition comprising polybutadiene binder inamounts from about 10 to about 24 percent by weight of said composition,inorganic oxidizer of ammonium perchlorate in amounts from about 50 toabout 72 percent by weight of said composition, alumi num metal powderin amounts from about 5 to about 15 percent by weight of saidcomposition, a burning rate catalyst comprising2,2-diphenylpicrylhydrazyl in amounts from about 0.5 to about 5 percentby weight of said composition, and lecithin in amounts from about 0.2 toabou 0.5 percent by Weight of said composition. a 2. The propellantcomposition of claim 1 and wherein said polybutadiene binder is carboxyterminated and is used in an amount of about 21.7 percent by weight ofsaid composition, said lecithin is used in an amount of about 0.3percent by weight of said composition, said inorganic oxidizer ofammonium perchlorate is used in an amount of about 63.4 percent byweight of said composition; said 63.4 percent being comprised of about19.0 percent by weight of 17 micron particle sized ammonium perchlorateand of about 44.4 percent by weight of 200 micron particle sizedammonium perchlorate, said burning rate catalyst2,2-diphenylpicrylhydrazyl is used in an amount of about 3.0 percent byweight of said composition, said aluminum metal powder is used in anamount of about 11.6 percent by weight of said composition and whereinsaid composition is cured by curatiyes selected from diaziridines,triaziridines, diepoxides, triepoxides, and combinations of the same,said curatives being used in amounts up to about 2 percent by weight ofall'the combined propellant ingredients.

3. The propellant composition of claim 1 wherein said compositioncontains an additional catalyst material selected from n-butyl ferroceneand F said additional catalyst material being used in amounts up toabout 5 percent by weight of said composition.

4. The propellant composition of claim 3 and wherein said polybutadienebinder is used in an amount of about 18.7 percent by weight of saidcomposition, said lecithin is used in an amount of about 0.3 percent byWeight of said composition, said additional catalyst material is nbutylferrocene which is used in an amount of about 3.0 percent by weight ofsaid composition, said aluminum metal powder is used in an amount ofabout 11.6 percent by Weight of said composition, said inorganicoxidizer of ammonium perchlorate is used in an amount of about 63.4percent by weight of said composition; said 63.4 percent being comprisedof about 19.0 percent by weight of 17 micron particle sized ammoniumperchlorate and of about 44.4 percent by weight of 200 micron particlesized ammonium perchlorate, and said burning rate catalyst 2,2-diphenylpicrylhydrazyl is used in an amount of about 3.0 percent byweight of said composition.

5. The propellant composition of claim 4 and wherein said polybutadienebinder is used in an amount of about 18.7 percent by weight of saidcomposition, said lecithin is used in an amount of about 0.3 percent byweight of said composition, said additional catalyst material is 'Fe Owhich is used in an amount of about 3.0 percent by weight of saidcomposition, said aluminum metal powder is used in an amount of about11.6 percent by weight of said composition, said inorganic oxidizer ofammonium perchlorate is used in an amount of about 63.4 percent byweight of said composition; said 63.4 percent being comprised of about19.0 percent by weight of 17 micron particle sized ammonium perchlorateand of about 44.4 percent by weight of 200 micron particle sizedammonium perchlorate, and said burning rate catalyst 2,2-diphenylpicrylhydrazyl is used in an amount of about 3.0 percent by weight ofsaid composition.

6. The propellant composition of claim 4 and wherein said polybutadienebinder is used in an amount of about 17.7 percent by weight of saidcomposition, said lecithin is used in an amount of about 0.3 percent byweight of said composition, said additional catalyst material is Fe Owhich is used in an amount of about 3.0 percent by weight of saidcomposition, said aluminum metal powder is used in an amount of about12.0 percent by weight of said composition, said inorganic oxidizer ofammonium perchlorate is used in an amount of about 64 percent by weightof said composition; said 64 percent being comprised of about 38.4percent by weight of 4 micron particle sized ammonium perchlorate and ofabout 25.6 percent by weight of 17 micron particle sized ammoniumperchlorate, and said burning rate catalyst 2,2-diphenylpicrylhydrazylis used in an amount of about 3.0 percent by weight of said composition.

7. The propellant composition of claim 4 and wherein said polybutadienebinder is used in an amount of about 19.7 percent by weight of saidcomposition, said lecithin is used in an amount of about 0.3 percent byweight of said composition, said additional catalyst material is Fe Owhich is used in an amount of about 3.0 percent by weight of saidcomposition, said aluminum metal powder is used in an amount of about12.0 percent by weight of said composition, said inorganic oxidizer ofammonium perchlorate is used in an amount of about 64 percent by weightof said composition; said 64 percent being comprised of about 38.4percent by weight of 4 micron particle sized ammonium perchlorate andsaid burning rate catalyst 2,2- diphenylpicrylhydrazyl is used in anamount of about 1.0 percent by weight of said composition.

*8. The propellant composition of claim 4 cured by curatives selectedfrom diaziridines, triaziridines, diepoxides, triepoxides, andcombinations of the same, said curatives being used in amounts up toabout 2 percent by weight of all the combined propellant ingredients.

References Cited UNITED STATES PATENTS 3,297,747 1/ 1967 Thornton 14936X BENJAMIN R. PADGE'IT, Primary Examiner US. Cl. X.R. 149-20, 36

